Normoxic is the name given to a breathing gas mix for which the percentage or fraction of oxygen is similar to the one of air, but contain a different mix of other gases. Along with hypoxic and hyperoxic, normoxic is one of the three kinds of breathing gas mixes for diving.
Hyperoxic is a term used for breathing gases that has a higher percentage or fraction of oxygen than regular air. The term or word is not so commonly used because of the designation Nitrox or Enriched Air, which is used instead to cover hyperoxic gases. It is the opposite of hypoxic.
Trimix is a mixture of three breathable gases. Oxygen, Nitrogen and Helium. It is used in technical diving to reduce the effects of nitrogen narcosis. Because helium has lower density, Trimix is also used to reduce the effort of breathing caused by surrounding pressure at greater depths.